LTC2955ITS8-2#TRMPBF

LTC2955 Pushbutton On/Off Controller with Automatic Turn-On Description Features n n n n n n n n n n Automatic Turn-On Via Voltage Monitor Input Wide Input Supply Range: 1.5V to 36V Low Supply Current: 1.2µA ±25kV ESD HBM on PB Input ±36V Wide Input Voltage for PB Input Low Leakage EN Output Allows DC/DC Converter Control (LTC2955-1) High Voltage EN Output Drives External P-Channel MOSFET (LTC2955-2) Simple Interface Allows Graceful µP Shutdown Adjustable Turn-Off Timer 10-Lead 3mm × 2mm DFN and 8-Lead ThinSOT™ Packages The LTC®2955 is a micropower, pushbutton on/off controller that manages system power by generating a clean enable output from the supply monitor input and the debounced pushbutton input. It features an interrupt output that notifies the system of a pushbutton or low supply event. When the system is ready, it may use the power kill input to shut off power. If the pushbutton remains pressed for more than the configurable turn-off duration, the system power is forced off. The supply input covers a wide range from 1.5V to 36V. The robust pushbutton input handles wide voltage swings of ±36V and ESD strikes to ±25kV (human body model) without latchup or damage. A low 1.2µA supply current maximizes battery run time. Separate versions are available for positive or negative enable polarities. Applications n n n n L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks and ThinSOT and PowerPath are trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners. Desktop and Notebook Computers GPS Devices Portable Instruments Automotive Electronics Typical Application Automatic Turn-On with Power-Fail Indication VTRIP = 5.4V LT3008-3.3 VOUT VIN 8.4V Pushbutton On/Off with Interrupt TURN ON PULSE 3.3V VIN 2.32M 402k 1M EN R7 1M EN LTC2955DDB-1 SEL INT ON PB TMR GND LONG PULSE PB SHDN 0.1µF SHORT PULSE KILL TURNS ON STAYS ON TURNS OFF µP INT PGD INTERRUPT POWER-FAIL INTERRUPT 2955 TA01b 2955 TA01a 2955fa For more information www.linear.com/LTC2955 1 LTC2955 Absolute Maximum Ratings (Note 1) VIN.............................................................. –0.3V to 40V Input Voltages PB............................................................ –40V to 40V ON.......................................................... –0.3V to 40V SEL......................................................... –0.3V to 40V KILL.......................................................... –0.3V to 6V Output Voltages EN/EN..................................................... –0.3V to 40V INT............................................................ –0.3V to 6V PGD.......................................................... –0.3V to 6V TMR....................................................... –0.3V to 2.7V Operating Temperature Range LTC2955C................................................. 0°C to 70°C LTC2955I..............................................–40°C to 85°C Storage Temperature Range................... –65°C to 150°C Lead Temperature (Soldering, 10 sec) TSOT-23 Package.............................................. 300°C Pin Configuration TOP VIEW INT 1 9 KILL 8 TMR VIN 4 7 SEL PB 5 6 GND *EN/EN 3 TOP VIEW 10 ON PGD 2 11 ON KILL TMR GND 8 7 6 5 INT EN/EN* VIN PB TS8 PACKAGE 8-LEAD PLASTIC TSOT-23 TJMAX = 125°C, θJA = 195°C/W *PIN 7 IS EN FOR LTC2955-1 AND IS EN FOR LTC2955-2 DDB PACKAGE 10-LEAD (3mm × 2mm) PLASTIC DFN TJMAX = 125°C, θJA = 55°C/W EXPOSED PAD (PIN 11) PCB GND CONNECTION OPTIONAL *PIN 3 IS EN FOR LTC2955-1 AND IS EN FOR LTC2955-2 Order Information 1 2 3 4 (http://www.linear.com/product/LTC2955#orderinfo) Lead Free Finish TAPE AND REEL (MINI) TAPE AND REEL PART MARKING* PACKAGE DESCRIPTION TEMPERATURE RANGE LTC2955CDDB-1#TRMPBF LTC2955CDDB-1#TRPBF LGBJ 10-Lead (3mm × 2mm) Plastic DFN 0°C to 70°C LTC2955CDDB-2#TRMPBF LTC2955CDDB-2#TRPBF LGBM 10-Lead (3mm × 2mm) Plastic DFN 0°C to 70°C LTC2955IDDB-1#TRMPBF LTC2955IDDB-1#TRPBF LGBJ 10-Lead (3mm × 2mm) Plastic DFN –40°C to 85°C LTC2955IDDB-2#TRMPBF LTC2955IDDB-2#TRPBF LGBM 10-Lead (3mm × 2mm) Plastic DFN –40°C to 85°C LTC2955CTS8-1#TRMPBF LTC2955CTS8-1#TRPBF LTGBK 8-Lead Plastic TSOT-23 0°C to 70°C LTC2955CTS8-2#TRMPBF LTC2955CTS8-2#TRPBF LTGBN 8-Lead Plastic TSOT-23 0°C to 70°C LTC2955ITS8-1#TRMPBF LTC2955ITS8-1#TRPBF LTGBK 8-Lead Plastic TSOT-23 –40°C to 85°C LTC2955ITS8-2#TRMPBF LTC2955ITS8-2#TRPBF LTGBN 8-Lead Plastic TSOT-23 –40°C to 85°C TRM = 500 pieces. *Temperature grades are identified by a label on the shipping container. Consult LTC Marketing for parts specified with wider operating temperature ranges. For more information on lead free part marking, go to: http://www.linear.com/leadfree/ For more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/. Some packages are available in 500 unit reels through designated sales channels with #TRMPBF suffix. 2 2955fa For more information www.linear.com/LTC2955 LTC2955 Electrical Characteristics The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VIN = 7V unless otherwise noted. (Note 2) SYMBOL PARAMETER CONDITIONS MIN TYP MAX UNITS Supply VIN Supply Voltage Range l 1.5 IIN VIN Supply Current l 0.5 VUVL VIN Undervoltage Lockout l VUVL(HYST) VIN Undervoltage Lockout Hysteresis l VPB(MIN(MAX)) PB Voltage Range l –36 VPB PB Input Threshold PB Falling l 0.6 VPB(HYST) PB Input Threshold Hysteresis (Note 3) VPB(VOC) PB Open Circuit Voltage I = –1µA l IPB PB Input Leakage Current 6V < PB < 36V PB = 1V PB = –36V l l l VON ON Threshold ON Rising l VON(HYST) ON Hysteresis DFN Package Only ION ON Input Leakage Current ON = 1V ON = 36V l l VKILL KILL Input Threshold Voltage KILL Falling l VKILL(HYST) KILL Input Threshold Hysteresis (Note 3) IKILL KILL Input Leakage Current VSEL SEL Input Threshold ISEL SEL Input Current SEL = 1V SEL = 36V l l VEN/EN(VOL) EN/EN Voltage Output Low I = 1mA l 1.5 VIN Rising 36 V 1.2 3 µA 1.0 1.15 1.3 V 30 85 200 mV 36 V 1 V Input Pins 0.8 40 3.0 mV 4.3 5.5 V –1 –4 ±10 –8 –400 µA µA µA 0.76 0.80 0.84 V 40 mV ±10 ±100 0.76 0.80 0.84 30 KILL = 1V l l 0.4 0.8 nA nA V mV ±50 nA 1.2 V ±50 ±100 nA nA 0.4 V Output Pins 0.175 VEN(VOH) EN Voltage Output High (LTC2955-1) I = 0µA, –0.5µA l VEN(VOH) EN Voltage Output High (LTC2955-2) I = 0µA, –0.5µA l VIN – 1.5 5.5 V IEN EN Pull-Up Current (LTC2955-1) EN = 0V l –1.2 –2 –2.8 µA IEN EN Pull-Up Resistance (LTC2955-2) l 0.45 0.9 1.35 MΩ VINT(VOL) INT Voltage Output Low I = 3mA l 0.4 V ±50 nA 5.5 V 0.4 V V IINT INT Leakage Current INT = 5V l VPGD(VOH) PGD Voltage Output High I = 0µA, –0.5µA l VPGD(VOL) PGD Voltage Output Low I = 3mA l IPGD PGD Pull-Up Current PGD = 0V l –1.2 –2 –2.8 µA ITMR(PU) TMR Pull-Up Current TMR = 0V l –2 –3 –4 µA ITMR(PD) TMR Pull-Down Current TMR = 1.5V l 2 3 4 µA 1.5 2955fa For more information www.linear.com/LTC2955 3 LTC2955 Electrical Characteristics The l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at TA = 25°C. VIN = 7V unless otherwise noted. (Note 2) SYMBOL PARAMETER CONDITIONS MIN TYP MAX tDB(ON) PB, ON Turn-On Debounce Time PB Falling or ON Rising → Enable Asserted tDB(OFF) PB Interrupt Debounce Time tTMR UNITS l 19 32 45 ms PB Falling → INT Falling l 19 32 45 ms Additional Turn-Off Debounce Time CTMR = 2200pF l 5.8 11.5 17.2 ms tINT(MIN) Minimum INT Pulse Width INT Falling → TMR Rising l 19 32 45 ms Timing tON(PD) ON Interrupt Delay ON Falling → INT Falling, VSEL > 0.8V l 200 µs tPGD(PD) PGD Propagation Delay ON Falling → PGD Falling l 200 µs tKILL(PD) KILL Propagation Delay KILL Falling → Enable Released l 60 µs tKILL(PW) KILL Minimum Pulse Width l 60 µs tKILL(ON BLANK) KILL Turn-On Blanking (Note 4) KILL Low, Enable Asserted → Enable Released l 304 512 720 ms tEN(LOCK OUT) Enable Released → Enable Asserted l 0.6 1 1.4 s EN/EN Lockout Time (Note 5) Note 4: The KILL turn-on blanking time is the waiting period immediately after the enable output is asserted. This blanking time allows sufficient time for the regulator and the µP to perform power-up tasks. The KILL, PB, and ON inputs are ignored during this period. Note 5: The enable lockout time is the waiting period immediately after the enable output is released. It allows an application to properly power-down such that the next power-up sequence starts from a consistent powered down configuration. PB and ON are ignored during this period. Note 1: Stresses beyond those listed under Absolute Maximum Ratings may cause permanent damage to the device. Exposure to any Absolute Maximum Rating condition for extended periods may affect device reliability and lifetime. Note 2: All currents into pins are positive; all voltages are referenced to GND unless otherwise noted. Note 3: Guaranteed by design, not subject to test. Typical Performance Characteristics Supply Current vs Temperature VIN = 7V, TA = 25°C, unless otherwise noted. Undervoltage Lockout vs Temperature Supply Current vs Supply Voltage 1.6 1.6 1.20 1.4 1.18 1.2 1.16 1.3 IVIN (µA) IVIN (µA) 1.4 1.2 1.1 1.0 VUVL (V) 1.5 1.0 0.8 0.8 –50 –25 50 25 0 75 TEMPERATURE (°C) 100 125 2955 G01 4 0.6 1.12 TA = –40°C TA = 25°C TA = 85°C 0.9 0 5 10 15 20 25 VIN (V) 30 35 1.14 40 2955 G02 1.10 –50 –25 50 25 0 75 TEMPERATURE (°C) 100 125 2955 G03 2955fa For more information www.linear.com/LTC2955 LTC2955 Typical Performance Characteristics ON/KILL Threshold vs Temperature VIN = 7V, TA = 25°C, unless otherwise noted. Turn-On Debounce Time vs Temperature 0.810 Additional Turn-Off Debounce Time vs TMR External Capacitance 36 10000 35 0.805 1000 0.800 tTMR (ms) tDB(ON) (ms) VON/KILL (V) 34 33 100 32 0.795 10 31 0.790 –50 –25 50 25 0 75 TEMPERATURE (°C) 100 30 –50 125 –25 50 25 0 75 TEMPERATURE (°C) 2955 G04 –3.4 5.0 –3.3 4.8 10 100 TMR EXTERNAL CAPACITANCE (nF) 1000 EN Output High Voltage vs Supply Voltage 5.0 4.0 –3.1 –3.0 –2.9 VEN(VOH) (V) 4.6 VEN(VOH) (V) ITMR(PU) (µA) 1 2955 G06 EN Output High Voltage vs Temperature –3.2 4.4 4.2 3.0 2.0 4.0 –2.8 1.0 3.8 –2.7 –2.6 –50 –25 50 25 0 75 TEMPERATURE (°C) 100 3.6 –50 125 –25 50 25 0 75 TEMPERATURE (°C) 2955 G07 VIN = 1.5V IPB (µA) 250 200 50 –50 –200 300 –160 250 –120 200 –80 –25 50 25 0 75 TEMPERATURE (°C) 100 125 2955 G10 3 4 VIN (V) 6 5 40 –40 –20 40 0 20 PB VOLTAGE (V) 7 150 100 50 0 100 2 PB Voltage vs External PB Resistance to Ground –40 VIN = 7V 150 1 2955 G09 PB VOLTAGE (mV) 400 300 0.0 125 PB Input Current vs PB Voltage I = 1mA 350 100 TA = –40°C TA = 25°C TA = 85°C 2955 G08 EN/EN Output Low Voltage vs Temperature VEN/EN(VOL) (mV) 1 125 2955 G05 TMR Pull-Up Current vs Temperature 450 100 2955 G11 0 TA = –40°C TA = 25°C TA = 85°C 50 20 0 10 30 40 EXTERNAL PB RESISTANCE TO GROUND (kΩ) 2955 G12 2955fa For more information www.linear.com/LTC2955 5 LTC2955 Pin Functions EN: Enable Output (LTC2955-1). EN is an active high output to control the turn-on/off of the system power. Connect this pin to the RUN or SHUTDOWN pin of the voltage regulator. The LTC2955 asserts EN high when the pushbutton is pressed or when ON goes high. The output high voltage follows the internal LDO output which provides sufficient margin for most SHUTDOWN pin thresholds. EN: Inverted Enable Output (LTC2955-2). EN is an active low output to control the turn-on/off of the system power. It may drive a voltage regulator’s active low enable input, or it may drive the gate of a P-channel MOSFET. In the turn-off state, the LTC2955 pulls this pin to VIN through an internal 900k resistor. The LTC2955 pulls EN to GND when the pushbutton is pressed or when ON goes high. Exposed Pad (DFN only): Exposed pad. Leave open or connect to device ground. GND: Device Ground. INT: Open Drain Interrupt Output. Connect this pin to the interrupt input of the system with a pull-up resistor to the system supply. The LTC2955 asserts the INT pin low when it receives the turn-off command from the pushbutton or the ON pin. The minimum pulse width of the INT signal is 32ms and can be extended through the TMR pin. KILL: Kill Input. A low at KILL releases the enable output (EN/EN). This pin can be driven by the microprocessor or it can be used as a voltage monitor input. Tie to the system power supply or an external voltage of 1.2V~5V if unused. ON: Monitor Input. Connect this pin to an external resistive divider from the monitored voltage. This allows automatic system turn-on when the monitored voltage transitions high. For the DFN part, if the SEL pin is tied high, it also allows automatic system turn-off when the monitored voltage transitions low. Tie to GND if unused. PB: Pushbutton Input. This is an active low input with a 900k pull-up to an internal LDO. Connect one terminal of the pushbutton to this pin and connect the other terminal of the pushbutton to GND. The pin may be left open if unused. PGD (DFN only): ON Status Output. A high on this pin indicates that the voltage at the ON pin is above the input threshold of 0.8V. This pin can be used as a system input to inform the system whether the turn-on was triggered by the ON pin or the pushbutton pin. Leave open if unused. SEL (DFN only): Mode Select Input. Connect SEL to GND to block the ON pin falling edge from activating system turn-off. Connect SEL to VIN to allow both the ON pin rising and falling edges to activate system turn-on and turn-off respectively. For the TSOT package, SEL is internally tied to GND. Do not leave open. TMR: Timer Pin. A capacitor to ground determines the additional time (5.2 seconds/μF) beyond the default 64ms that the pushbutton must be held low before immediately releasing the EN/EN and INT outputs. The turn-off debounce time defaults to 64ms if this pin is left open. To disable the ability to force a system power-down with a pushbutton press, ground the TMR pin. VIN: Power Supply Input. For > 20V applications, connect VIN to the power source through a 1k resistor and bypass VIN to GND with a 10nF low ESR capacitor. 6 2955fa For more information www.linear.com/LTC2955 LTC2955 Block Diagram VIN 900k EN (2955-2) VLDO EN CONTROL 2µA LTC2955-2 VIN REGULATOR VLDO ≈ 5.2V EN (2955-1) EN CONTROL VLDO 900k PB 0.8V EN CONTROL – VLDO LOGIC 2µA DEBOUNCE + OSCILLATOR ON ON LTC2955-1 OSCILLATOR f = 1kHz PGD* + OFF 0.8V INT – + GND TMR + SEL* – – 0.8V KILL 0.8V 2955 BD *DFN ONLY 2955fa For more information www.linear.com/LTC2955 7 LTC2955 Operation Overview The LTC2955 is a pushbutton on/off controller that manages system power based on a pushbutton input (PB pin) and a voltage monitor input (ON pin). In a typical application, the enable output (EN/EN) turns on system power when the pushbutton is pressed or the supply monitor detects the presence of a primary or secondary supply such as a wall adaptor or car battery. After the system is powered up, a pushbutton event asserts the interrupt output (INT) which can be used in menu driven applications to request for a system power-down. A power kill input (KILL) allows a microprocessor or system to release the enable output immediately, effectively powering down the system. System power is also forced off if the pushbutton remains asserted for more than the forced turn-off activation time configurable via the TMR pin. The LTC2955 is also designed with a blanking time after each system turn on and off event. During this blanking time, the LTC2955 ignores the KILL, ON and PB pins, thus ensuring that the system stays on/off for a minimum amount of time. This provides sufficient time for the voltage regulator to turn on/off and allows it to charge/discharge its output to the final voltage. It also allows the µP sufficient time to perform power on/off tasks. The PGD output indicates the status of the ON pin to allow the system to differentiate between pushbutton turn-on or supply plug-in events. Turn-On Sequence and KILL Blanking Time The LTC2955-1 asserts the EN output high if the pushbutton is pressed or the ON pin goes high. This is typically used to turn on a DC/DC converter or linear regulator. Figure 1 shows the turn-on sequence of the LTC2955-1 initiated by the PB pin. When the button is pressed at time t1, a high to low transition on the PB pin initiates the turnon sequence. The PB pin must stay low continuously for a period of 32ms (tDB(ON)) before the LTC2955-1 asserts the EN output high. Once EN goes high (t2), an internal 512ms blanking time (t KILL(OnBlank)) is started. During this blanking time, the LTC2955-1 ignores the KILL, ON and PB pins and keeps EN high for at least 512ms. This provides sufficient time for the voltage regulator to turn on and charge its output to the final voltage and allows the µP enough time to perform power on tasks. The µP must pull the KILL pin high during this 512ms blanking time, or else EN will go low at the end of this time (t3). t2 t1 t3 PB AND KILL IGNORED PB tDB(ON) tKILL(ON BLANK) EN (LTC2955-1) 2955 F01 Figure 1. Pushbutton Turn-On Timing 8 2955fa For more information www.linear.com/LTC2955 LTC2955 Operation A high to low transition on PB (t1) starts the turn-off sequence. In order to assert INT (interrupt output) low, PB must stay low continuously for 32ms (tDB(OFF)). At the end of the 32ms (t2), the INT pin is asserted low and will stay low for at least 32ms (tINT(MIN)), even if the PB pin goes high during this period (t2 to t4). When the µP receives this interrupt signal, it should start to perform its power-down functions and assert KILL low (t3) once it is done. The LTC2955-1 will then release INT and pull EN low, thus turning off the system power, as shown with dotted lines in Figure 3. At the end of this blanking time, the LTC2955-1 will check that the PB pin is high. If the PB pin remains low, it will be ignored until a high is detected on the pin. The next low on the PB pin will initiate a turn-off sequence. Figure 2 shows a similar LTC2955-1 turn-on sequence with the ON pin going high. The timing sequence is very similar to that initiated by the pushbutton. The PGD output follows the ON pin. PB Pin Turn-Off Sequence Figure 3 shows the turn-off sequence of the LTC2955-1 initiated through the PB pin. A turn-off sequence refers to the LTC2955-1 releasing the EN output. This turns off the voltage regulator. The user can also force the system to power-down if the µP fails to respond to the interrupt signal (KILL pin remains t2 t1 t3 ON AND KILL IGNORED ON tKILL(ON BLANK) tDB(ON) EN (LTC2955-1) PGD 2955 F02 Figure 2.ON Pin Turn-On Timing t1 t2 t3 t4 t5 t6 PB IGNORED PB t7 PB IGNORED tDB(OFF) tEN(LOCKOUT) IGNORED KILL 16 CYCLES TMR tTMR INT tINT(MIN) EN (LTC2955-1) 2955 F03 Figure 3. Pushbutton Turn-Off Timing 2955fa For more information www.linear.com/LTC2955 9 LTC2955 Operation high). This can be done by holding the pushbutton down for a long period (> tDB(OFF) + tINT(MIN) + tTMR) as shown with the solid lines in Figure 3. If the PB pin remains low at the end of the 32ms minimum INT pulse width (tINT(MIN)), the external timer will start counting (t4). The capacitance at the TMR pin determines the duration of this timer and it will count for 16 cycles (tTMR). If the PB pin remains low at the end of the 16 cycles (t5), the LTC2955-1 will force the EN pin low and the INT pin high. See Applications Information for adjusting tTMR. After the EN output goes low and the PB pin goes high, the LTC2955-1 starts the one second lockout time (tEN(LOCKOUT)). During this lockout time (t6 to t7 in Figure 3) the PB and ON inputs are ignored. This is to allow time for the voltage regulator to turn off and for its output to decay to 0V. This ensures that the µP has completely powered down before it is allowed to restart. After the one second lockout time, the LTC2955-1 proceeds to the next stage to wait for a turn-on command and the cycle will repeat as above. If the PB pin remains low after the EN output goes low, the LTC2955-1 will delay the start of this lockout time until the PB pin goes high. If the PB pin goes high when the external timer is still counting, as shown in Figure 4, the turn-off sequence will be aborted. The INT pin is forced high immediately and the EN pin remains high. PB IGNORED PB tDB(OFF) t < tTMR TMR INT 2955 F04 tINT(MIN) Figure 4. Pushbutton Turn-Off Aborted 10 2955fa For more information www.linear.com/LTC2955 LTC2955 Operation ON Pin Turn-Off Sequence (DFN Package Only) to perform power-down functions. The INT pin will stay low for at least 32ms (tINT(MIN)). When the µP receives this interrupt signal, it should start to perform its powerdown functions and assert the KILL input low (t2) once it is done. The LTC2955-1 will then release the EN and INT outputs, thus turning off the system power, as shown with dotted lines in Figure 5. Figure 5 shows the turn-off sequence of the LTC2955-1 initiated by the ON pin. The timing sequence is slightly different from that by the pushbutton as there is no debounce time (tDB(OFF)) before the INT pin pulls low. The ON pin falling edge can start the turn-off sequence only if the following two conditions are met: (1) The preceding turn-on sequence was initiated by the ON pin rising edge, and (2) The SEL pin must be tied high (>0.8V). For TS8 package, the ON pin falling edge is ignored. If the µP fails to respond (KILL pin remains high, as shown with solid line in Figure 5) and the ON pin remains low 32ms after INT goes low, the external timer will start counting for 16 cycles (tTMR, t3 to t4). If the ON pin remains low at the end of the 16 cycles (t4), the LTC2955-1 will force the EN pin low and the INT pin high. See Applications Information for adjusting tTMR. In Figure 5, a high to low transition at ON (t1) starts the turn-off sequence. The interrupt output (INT) is asserted immediately when the ON pin goes low. Unlike the PB pin turn-off sequence, there is no 32ms debounce time (tDB(FF)) for the ON pin going low. This allows the system to initiate a shutdown as soon as the monitored supply is removed and allows the µP the maximum amount of time t1 After the EN output goes low, the LTC2955-1 starts the one second lockout time (tEN(LOCKOUT)). During this lockout time (t4 to t5), the PB and ON inputs are ignored. t2 t3 t4 t5 IGNORED ON tINT(MIN) IGNORED KILL 16 CYCLES TMR tTMR INT tEN(LOCKOUT) EN (LTC2955-1) PGD 2955 F05 Figure 5. ON Pin Turn-Off Timing (DFN Only, VSEL > 1.2V and the Preceding Turn-On Sequence Was Initiated by the ON Pin Rising Edge 2955fa For more information www.linear.com/LTC2955 11 LTC2955 Operation PB vs ON Pin With the DFN package, if the turn-on sequence is initiated by the pushbutton, the ON input is ignored until the pushbutton is pressed again to initiate a turn-off sequence. As shown in Figure 6, the PB pin initiates a turn-on sequence at time t1 before the ON pin goes high at time t2. Once EN goes high (t3), the ON input is ignored, so a falling edge at the ON pin (t4) will not initiate a turn-off sequence even if the SEL pin is high. This allows the system to remain powered up if it is plugged in and out of a secondary power source while the system is already turned on. If the turn-on sequence is initiated by the ON pin, both the pushbutton and the ON pin falling edge can initiate the turn-off sequence. For the TS8 package, ON pin falling edge is always ignored regardless of which pins initiate the turn-on. The PB pin has priority over the ON pin, so if the PB pin goes low and ON pin goes high at the same time, the LTC2955-1 will monitor the PB pin for the 32ms debounce time and ignore the ON pin unless the PB pin bounces during the 32ms. ON Pin Initial Turn-On If the LTC2955-1 powers up with the ON pin already high, the EN pin will go high after a power-up delay of about one second. Subsequently, if the pushbutton is pressed to force EN low, the LTC2955-1 will not initiate another turn-on even if the ON pin remains high. The LTC2955-1 needs a rising edge at the ON pin or a falling edge on the PB pin to initiate the subsequent turn-on. ON PIN IS IGNORED, SINCE PUSHBUTTON IS PRESSED FIRST t1 t2 ON GOING LOW IS IGNORED, SINCE THE EN IS ASSERTED BY THE PUSHBUTTON t3 t4 t5 ON PIN PB PIN PGD PIN TURN-ON BY PB EN PIN 2955 F06 Figure 6. Pushbutton Is Pressed Before the ON Pin Goes High 12 2955fa For more information www.linear.com/LTC2955 LTC2955 Operation As shown in Figure 7, if the ON pin is high when power is first applied to the LTC2955-1 at time t1, the EN pin will go high (at t2) after the one second EN lockout time. At time t3, the pushbutton is pressed to activate turn-off while the ON pin remains high. The LTC2955-1 will wait for a rising edge at the ON pin or a low at the PB pin to activate the next turn-on. As shown at time t4, after the one second lockout time, the EN stays low with ON high. At time t5, only the rising edge of the ON pin or a PB event will trigger the next turn-on again. LTC2955-1, LTC2955-2 Versions The LTC2955-1 and LTC2955-2 differ only by the polarity of the high voltage (36V absolute maximum) enable pin. The LTC2955-1 EN pin is a high true output designed to drive the SHUTDOWN pin of most voltage regulators. In turn-on mode, this pin is pulled high by a pull-up current of 2µA powered by an internal LDO, which gives a high level output voltage (VOH) of typically 4.3V. In turn-off mode, this pin is pulled low by an internal N-channel MOSFET. If a higher VOH or higher pull-up current is required, connect the EN pin to an external source through a pull-up resistor. The LTC2955-2 EN pin is a low true enable output designed to drive the gate of an external P-channel MOSFET. In turn-on mode, the EN pin is pulled low by an internal N-channel MOSFET. In turn-off mode, this pin is pulled high to VIN through an internal 900k resistor. An external pull-up resistor can be connected between this pin and VIN to increase the pull-up current. POWER FIRST APPLIED TO LTC2955 VIN PIN t1 t2 VIN t3 t4 A HIGH AT ON PIN IS IGNORED AFTER THE FIRST TURN-ON/OFF SEQUENCE t5 ON RISING EDGE ON PIN TURN-OFF BY PUSHBUTTON PB PIN TURN-ON BY ON HIGH LEVEL TURN-ON BY ON RISING EDGE EN PIN 2955 F07 tEN(LOCKOUT) tEN(LOCKOUT) Figure 7. Power First Applied to LTC2955-1 2955fa For more information www.linear.com/LTC2955 13 LTC2955 Applications Information Adjusting the Forced Turn-Off Timing Voltage Monitoring with KILL Input The LTC2955 allows the user to force the system power to turn off if the µP fails to respond during fault conditions. As shown by the solid lines in Figure 3 and Figure 5, when the µP fails to bring the KILL pin low after the interrupt signal is asserted, the user can force a turn-off by holding down the pushbutton. The length of time that PB must be held low is given by a fixed 64ms delay (tDB(OFF) + tINT(MIN)) plus an adjustable power-down timer delay (tTMR). The adjustable delay is set by placing an optional external capacitor on the TMR pin. Use the following equation to calculate the capacitance for the desired delay. CTMR is the external capacitor at the TMR pin: The KILL pin can also be used as a voltage monitor input. Figure 8 shows an application where the KILL pin has a dual function. It is driven by a low leakage open drain output of the µP. It is also connected to a resistive divider that monitors battery voltage (VIN). When the battery voltage falls below the set value, the voltage at the KILL pin falls below 0.8V and the EN pin is quickly pulled low. Note that the resistor values should be as large as possible, but small enough to keep leakage currents from tripping the 0.8V KILL comparator. CTMR = 0.19 • tTMR [µF/sec] If there is no circuitry available to drive the KILL pin, this pin can be connected to a voltage regulator output through a resistive divider or RC network as shown in Figure 9. The KILL pin acts as a voltage monitor pin that shuts down the regulator when its output voltage drops below a certain level. As an example, if the required turn-off debounce time is one second: tTMR = (1000ms – 64ms) CTMR = 0.19 • 0.936 Required CTMR is 0.178µF The ON pin turn-off debounce time is 32ms less than the PB pin debounce time since there is no tDB(OFF). If the TMR pin is left open, the turn-off debounce time defaults to 64ms for the PB pin and 32ms for the ON pin. Operation Without µP The minimum pulse width needed to trigger KILL is 30µs. If there are glitches on the resistor pull-up voltage that are wider than 30µs and transition below 0.8V, then an appropriate bypass capacitor should be connected to the KILL pin. VIN = 9V VIN = 9V VIN VIN VOUT LT3060 R3 583k 1% VOUT VOUT LT3060 VOUT SHDN SHDN R1 10k R2 100k 1% C4 0.1µF EN VIN LTC2955TS8-1 INT PB ON INT µP KILL (OPEN DRAIN) KILL GND C4 0.1µF R1 10k TMR EN VIN LTC2955TS8-1 INT PB KILL ON GND + TMR CTMR* 1µF *OPTIONAL 2955 F08 CTMR* 1µF *OPTIONAL C3* 0.01µF 2955 F09 Figure 9. Application without µP Figure 8. Input Voltage Monitoring with KILL Input 14 2955fa For more information www.linear.com/LTC2955 LTC2955 APPLICATIONS INFORMATION High Voltage PowerPath™ Switching capacitor at the pin lessens the impact of this coupling. The parasitic series inductance may cause unpredictable ringing at the PB pin; placing a 5.1k resistor from the PB pin to the pushbutton switch reduces this ringing. Figure 11 shows an example of this RC network at the PB pin. The high voltage EN open drain output of the LTC2955-2 is designed to switch on/off an external power P-channel MOSFET. This allows a user to connect/disconnect a power supply (or battery) to its load by toggling the PB pin. Figure 10 shows the LTC2955-2 controlling a two cell Li-Ion battery application. The KILL pin is connected to the output of the external MOSFET through a resistive divider. The KILL pin serves as a voltage monitor. When VOUT drops below 6V, the EN pin is pulled high (to VIN) after 15µs later. R9 slows down the turning on of M1 so as to limit the inrush current when M1 turns on to charge up the capacitor at VOUT. R5 helps to speed up the turning off of M1 and also to keep M1 off when the input voltage rise time is fast. External Pull-Up Resistor on PB Pin An internal 900k pull-up resistor on the PB pin makes an external pull-up resistor unnecessary. Leakage current on the PB board trace, however, will affect the open circuit voltage on the PB pin. If the leakage is too large (>1µA), the PB voltage may fall close to the threshold window. To VIN PARASITICS TRACE CAPACITANCE PB Pin in a Noisy Environment The rugged PB pin is designed to operate in noisy environments. Transients below ground and above VIN (–36V < VIN < 36V) will not damage the rugged PB pin. Additionally, the PB pin can withstand ESD HBM strikes of up to ±25kV. VIN R6 5.1k PB NOISE C5 0.1µF TRACE INDUCTANCE + 4.2V SINGLE CELL Li-ION BATTERY R9 100k VOUT PB KILL GND VOUT,TRIP POINT = 6V R1 649k 1% EN VIN LTC2955TS8-2 INT ON TMR Figure 11. Noisy PB Trace R5* 100k C4 0.1µF KILL GND DETAILS OMITTED FOR CLARITY M1 4.2V SINGLE CELL Li-ION BATTERY INT 2955 F11 However, if the pushbutton switch is located physically far from the LTC2955 PB pin, the parasitic capacitance and parasitic series inductance of the connecting cable or PCB trace can create problems. The parasitic capacitance can couple external noise onto the PB input; placing a 0.1µF + EN LTC2955-1 VTH = 0.8V INPUT TMR CTMR* 0.033µF OPTIONAL GLITCH FILTER CAPACITOR R4 100k 1% *OPTIONAL C3* 0.1µF 2955 F10 Figure 10. PowerPath Control with 6V Undervoltage Detect 2955fa For more information www.linear.com/LTC2955 15 LTC2955 APPLICATIONS INFORMATION mitigate the effect of the board leakage, a 10k resistor to VIN is recommended (see Figure 12). LTC2955-1/ LTC2955-2 VIN VIN VLDO R7 10k 900k The maximum operating current of the LTC2955 is less than 3µA, creating an insignificant voltage drop across the resistor. Using a capacitor value of 10nF provides sufficient filtering for most applications and larger values can actually diminish its effectiveness. PB 0.8V >2µA GND EXTERNAL BOARD LEAKAGE CURRENT 2955 F12 IF EXTERNAL PARASITIC BOARD LEAKAGE >2µA USE EXTERNAL PULL-UP RESISTOR Adding a 10nF capacitor in addition to the 1k resistor can protect against high voltage input transients that would exceed the 40V Absolute Maximum Voltage rating of the VIN pin. These could occur during hot-plugging into a battery or AC adapter. This can also protect against transients that may appear on the PCB ground during large ESD strikes at the PB pin. PINS OMITTED FOR CLARITY Applications with Slide Switch Figure 12. External Pull-Up Resistor on PB Pin Enhancing VIN Ruggedness Placing a 1k resistor and a 10nF capacitor at the VIN pin can be used to enhance ruggedness in some applications. A 1k resistor in series with the VIN pin allows the LTC2955 to withstand reverse-input voltages. The LTC2955’s VIN pin is internally clamped to one diode voltage below ground. In battery operated applications where a battery could be inserted improperly, this resistor will limit the current and allow internal clamping to protect the pin. In some applications, to prevent accidental toggling of the system power, a slide switch is preferred over a pushbutton. Figure 14 shows a slide switch added in series with the pushbutton. The user can slide the switch open to activate the HOLD/LOCK function, where the pushbutton is disabled. Figure 15 shows a slide switch connected to the LTC2955 ON pin resistive divider. If the user slides the switch to the ON position, the LTC2955 ON pin is high VIN ON SEL HOLD/LOCK + VIN EN VIN LTC2955DDB-1 PB VOUT GND NORMAL 2955 F14 LT3060 9V BATTERY SHDN R8 1k C4 10nF EN VIN LTC2955TS8-1 INT PB GND R1 10k INT KILL KILL TMR Figure 14. Using a Slide Switch to Prevent Accidental Turn-On/Off µP VIN VIN OFF ON 2955 F13 EN SEL ON ON CONT* 0.033µF LTC2955DDB-1 PB *OPTIONAL GND 2955 F15 Figure 13. Enhancing VIN Ruggedness 16 Figure 15. Using a Slide or Toggle Switch to Turn-On/Off 2955fa For more information www.linear.com/LTC2955 LTC2955 APPLICATIONS INFORMATION and the device turns on. If the user slides the switch to the OFF position, the ON pin voltage drops to 0V and the LTC2955 activates a turn-off since the SEL pin is high (DFN package only). Interface with Switching Regulators The LTC2955-1 EN pin can be connected directly to most switching regulator SHUTDOWN inputs. The EN pin high level output voltage (VEN(VOH)) is typically 4.3V with VIN >5V, and VEN(VOH) = VIN – 0.5V if VIN